Method and system for forming LED light emitters

ABSTRACT

A flexible sheet of light-emitting diode (LED) light emitters includes a support substrate having a thermally conductive material. The flexible sheet of LED light emitters also has an LED emitter sheet overlying the support substrate, and the LED emitter sheet including a plurality of LED light emitters. The flexible sheet of LED light emitters also has a flexible circuit sheet overlying the LED emitter sheet, and a phosphor sheet overlying the flexible circuit sheet. The phosphor sheet includes a wave-length converting material. The flexible sheet of LED light emitters also has a lens sheet overlying the phosphor sheet. The lens sheet includes a plurality of lenses.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/539,863, filed Nov. 12, 2014, now U.S. Pat. No.9,041,024, which is a divisional patent application of U.S. patentapplication Ser. No. 13/781,095, filed Feb. 28, 2013, now U.S. Pat. No.8,912,023, which claims priority to U.S. Provisional patent applicationSer. No. 61/606,355, filed Mar. 2, 2012. All of the above applicationsare commonly owned and incorporated by reference herein in theirentirety. This application is also related to co-pending and commonlyowned U.S. patent application Ser. No. 12/420,802, filed Apr. 8, 2009,entitled “Total Internal Reflection Lens And A Mechanical Retention AndLocating Device,” U.S. patent application Ser. No. 12/756,861, filedApr. 8, 2010, entitled “Package for Multiple Light Emitting Diodes,” andU.S. patent application Ser. No. 13/106,808, filed May 12, 2011,entitled “Tuning Of Emitter With Multiple LEDs To A Single Color Bin.”The disclosures of all of the above applications are incorporated byreference herein in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates in general to lighting devices based onlight-emitting diodes (LEDs) and the methods for manufacture.

Lighting devices based on LEDs are becoming more popular. As the demandsfor these lighting devices continue to increase, the cost of the LEDdice have been decreasing. On the other hand, the cost of othercomponents in the LED emitter makes it difficult to lower the over-allsystem cost. In order for LED-based lighting devices to satisfy therequirement of various potential applications, the over-all system costneeds to be reduced. Therefore, the need for cost-effectivemanufacturing techniques is becoming more critical in LED-based lightingdevices.

BRIEF SUMMARY OF THE INVENTION

As the price of LED dice continue to drop, conventional methods ofmanufacturing LED light emitters are limited by the cost of othercomponents and the cost of assembly the lighting devices as a whole. Forexample, the LED die are usually disposed on a substrate, which provideselectrical connection and thermal conduction. The LED die and substrateare usually mounted on an MCPCB (metal-core printed circuit board),which has been widely used in packaging LED light emitters. The cost ofpackaging individual emitters often becomes a substantial part of theover-cost the LED emitters.

According to embodiments of the present invention, a method for formingmultiple LED emitters includes using sheets of materials, including lenssheet, phosphor sheet, connector sheet, LED and substrate sheet, etc.The assembled sheets are then singulated to form individual emittersthat can be interconnected by flexible and/or stretchable sheets.

According to an embodiment of the present invention, a method forforming a flexible sheet of LED light emitters includes forming a microlens sheet having a plurality of lenses, forming a phosphor sheetincluding a wave-length converting material, forming a flexible circuitsheet of conductive patterns, forming a ceramic substrate sheetincluding a plurality of LED light emitters, and forming a supportsubstrate including a thermally conductive material. The method alsoincludes attaching the above sheets to form a stack including, from topto bottom, the lens sheet, the phosphor sheet, the flexible circuitsheet, the ceramic substrate sheet, and the support substrate.

In some embodiments, the method includes forming the stack of sheetsusing thermal energy. In other embodiments, the method includes formingthe stack of sheets using mechanical pressure.

In some embodiments of the above method, the micro lens sheet includes aglass material. In some embodiments the micro lens sheet comprises aplurality of preformed notches or cracks. In an embodiment, the flexiblecircuit sheet includes conductive lines and solder joints formed on aflexible and stretchable material.

In other embodiments, the ceramic substrate sheet includes a pluralityof preformed notches or cracks. In some embodiments, the method alsoincludes simulating the flexible sheet of LED light emitters by breakinglens sheet at the preformed notches or cracks. In some embodiments, themethod also includes singulating the flexible sheet of LED lightemitters by passing the flexible sheet through one or more rollers. Insome embodiments, the flexible sheets are also stretchable, and theconductive wires can be formed in zig-zag shape.

According to another embodiment of the present invention, a flexiblesheet of LED light emitters includes a support substrate including athermally conductive material, a ceramic substrate sheet overlyingsupport substrate. The ceramic substrate sheet includes a plurality ofLED light emitters. The flexible sheet of LED light emitters alsoincludes a flexible circuit sheet overlying the substrate sheet, and aphosphor sheet overlying the flexible circuit sheet, the phosphor sheetincluding a wave-length converting material. The flexible sheet of LEDlight emitters also includes a lens sheet overlying the phosphor sheet.The lens sheet includes a plurality of lenses.

In some embodiments, the flexible sheet of LED light emitters is alsostretchable. Each of the plurality of lenses in the lens sheet isaligned to a corresponding one of the plurality of LED light emitters.In some embodiments, the lens sheet includes pre-formed notches orcracks between adjacent lenses.

In some embodiments, the ceramic substrate includes pre-formed notchesor cracks between adjacent emitters. In some embodiments, the lens sheetincludes separate lenses. In certain embodiments, the ceramic substrateincludes separate LED emitters.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the component of a flexible sheet of LED emitters accordingto an embodiment of the present invention;

FIG. 2 illustrates an assembled sheet of LED emitters according to anembodiment of the present invention;

FIG. 3 illustrate a method for singulating the emitters from a sheet ofemitters; and

FIG. 4 illustrates a flexible sheet of LED emitters after singulationaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The description below is presented with reference to a series of drawingfigures enumerated above. These diagrams are merely examples, and shouldnot unduly limit the scope of the claims herein. In connection with thevarious aspects illustrated and described, one of ordinary skill in theart would recognize other variations, modifications, and alternatives.

FIG. 1 shows the components of a flexible sheet of LED emittersaccording to an embodiment of the present invention. As shown, thecomponents of a flexible sheet of LED emitters 100 include a lens sheet110, a phosphor sheet 120, a flexible circuit sheet 130, an emittersheet 140 which can include a ceramic substrate sheet with embeddedLEDs, and a flexible support substrate 150. These components aredescribed in more details below.

Lens sheet 110 includes a sheet of transparent material with lenses 112.The transparent material can be an optically transparent materialsuitable for forming lenses. For example, glass or silicone can be usedto form the lens sheet. In some embodiments, the lens sheet is made bymolding glass or silicone, and the lenses can be formed integrally withthe sheet. As shown in FIG. 1, lens sheet is a connected sheet withlenses formed therein.

In a conventional LED emitter, a primary lens is usually used to extractlight from the LED die, and a secondary lens is often used for beamforming purposes. In some cases, the primary lens may form part of theemitter, and the secondary lens may be part of a housing. Examples oflenses are described in U.S. patent application Ser. No. 12/420,802,filed Apr. 8, 2009, entitled “Total Internal Reflection Lens And AMechanical Retention And Locating Device.” In some embodiments of thepresent invention, the lens can perform the functions both the primarylens and secondary lens, i.e., both light extracting and beam forming.In some embodiments, the lens sheet is made from silicone, and the sheetcan remain flexible. In some embodiments, a glass lens sheet is used totake advantage of the better heat conductive properties of glass thansilicone. Lens sheets made from glass can be rigid. In some embodiments,preformed notches or cracks 114 are formed in the lens sheet tofacilitate singulation as described below. In an example, these notchesor cracks can be made by laser. In other example, the notches or crackscan be formed by a mechanical method. In some examples, notches orcracks are formed on both front and back sides of the sheet andpenetrate partially into the sheet. In other examples, the notches orcracks can be formed on only the front side or the back side.

In FIG. 1, phosphor sheet 120 is for light wavelength conversion.Phosphor sheet 120 in combination with the emitters in emitter sheet 140allows the emission of desirable light colors. For example, light from ablue LED passing through a yellow phosphor can produce a white light. Insome embodiments, the phosphor sheet can include a mixture of phosphors,for example, yellow and red phosphors. In some embodiments, the phosphorparticles are uniformly distributed in a base material of, e.g.,silicone. The phosphor sheet can be pre-formed and then attached to atarget sheet. Alternatively, the phosphor sheet can be formed on atarget sheet, for example, by painting.

Flexible circuit sheet 130 includes conductive lines that make contactsto the LED emitters in emitter sheet 140. In some embodiments, flexiblecircuit sheet 130 can include a flexible plastic sheet made of, e.g.,polyimide or polyester, etc. In some embodiments, circuit sheet 130 caninclude conductive patterns formed in the sheet or over the sheet, andcan also include solder joints or connectors. The flexible material canprotect solder joints, electrical contacts, and wires that are formed onthe sheet or embedded in the sheet. The conductive patterns may beprinted on the plastic sheet.

In some embodiments, circuit sheet 130 can be made of a stretchablematerial, for example, a polymer such as polyimide. In some embodiments,the conductive wires can be made in zig-zag shapes to allow stretching.The stretching may occur during manufacturing (e.g., roller forsimulation) or in actual use (e.g., when extended to cover a non-planartarget area). As described below, circuit sheet 130 is also configuredto allow access and control of individual LED dice.

In FIG. 1, LED emitter sheet 140 includes multiple LED emitters 142built on a substrate. In some embodiments, the substrate is a ceramicsubstrate sheet configured to accommodate multiple emitters, whereineach emitter can have multiple embedded LED dice. In embodiments of theinvention, these LED dice are inorganic solid-state based LED lightsources. In some embodiments, the substrate includes a stack of multiplelayers for providing improved heat conduction and electrical contacts.In some embodiments, the design of the substrate allows individual LEDdie in an emitter to be separately addressable. Along with the flexibleand, in some cases, stretchable circuit sheet 130, this arrangementallows tuning of the light color. Examples of substrate and emitters andlight tuning are described in U.S. patent application Ser. No.12/756,861, filed Apr. 8, 2010, entitled “Package for Multiple LightEmitting Diodes,” and U.S. patent application Ser. No. 13/106,808, filedMay 12, 2011, entitled “Tuning Of Emitter With Multiple LEDS To A SingleColor Bin.” The disclosures of all of the above applications areincorporated by reference herein in their entirety.

The ceramic substrate sheet tend to be rigid. In some embodiments,pre-formed notches or cracks 144 are formed in the substrate allowsingulation. Similar to the notches or cracks described above inconnection with the lens sheet, the notches or cracks in the substratecan be made by laser. In other example, the notches or cracks can beformed by a mechanical method. In some examples, notches or cracks areformed on both front and back sides of the sheet and penetrate partiallyinto the sheet. In other examples, the notches or cracks can be formedon only the front side or the back side. In some embodiments, noelectrical contacts are formed at the bottom layer.

In FIG. 1, sheet 150 is a support substrate, for example, a sheet ofthermal pad, which is thermally conductive for heat dissipation. Thematerial for sheet 150 can be selected from conventional thermalinterface material (TIM). In some embodiments, sheet 150 can be disposedon a heat sink. Sheet 150 can also include a protective layer. In someembodiments, no back-side electrical contacts to the emitters areprovided.

According to another embodiment of the invention, the sheets describedabove can be made separately. These sheets are then stacked together,e.g., by lamination, to form an assembled sheets of LED emitters. In anembodiment, a method for forming a flexible sheet of LED light emittersincludes forming the individual sheets, which can include:

-   -   forming a lens sheet having a plurality of micro lenses;    -   forming a phosphor sheet including a wave-length converting        material;    -   forming a flexible circuit sheet;    -   forming a ceramic substrate sheet including a plurality of LED        light emitters; and    -   forming a support substrate including a thermally conductive        material.        In some embodiments, these sheets are then brought together to        form a stack including, from top to bottom, the lens sheet, the        phosphor sheet, the flexible circuit sheet, the ceramic        substrate sheet, and the support substrate. In other        embodiments, one or more sheets can be omitted, or disposed in a        different position. For example, in some embodiments a flexible        circuit sheet can be formed below the LED sheet, instead of        above the LED sheet. In other embodiments, a flexible circuit        sheet can be formed above and below the LED sheet to provide        electrical connections.

FIG. 2 illustrate an assembled sheet of LED emitters 200, including alens sheet 110, a phosphor sheet 120, a flexible circuit sheet 130, anLED sheet 140 which includes a ceramic substrate sheet with embeddedLEDs, and a flexible support substrate 150, which are described above inconnection with FIG. 1. These sheets are attached together to form thesheet of LED emitters 200 using thermal energy or mechanical pressure.The attachment can also be accomplished by lamination methods.

FIG. 3 illustrate a method for singulating the emitters from a sheet ofemitters. As shown, a flexible sheet of emitter 310 is passed throughrollers 320 and 330. The pressure from the rollers causes the pre-formednotches or cracks in the micro-lens sheet 110 and the ceramic sheet 140to break into multiple pieces, which are held together by flexiblesheets 120, 130, and 150. As a result, the sheet of emitter 310 becomesflexible. As described above, sheets 120, 130, and 150 can be flexibleand stretchable. Depending on the embodiments, one or more rollers maybe used in the singulation step.

FIG. 4 illustrates a flexible sheet of LED emitters after singulationaccording to an embodiment of the present invention. As can be seen inFIG. 4, lens sheet 110 and the emitter substrate sheet 140 includeindividual lenses 112 and emitters 142 separated in the singulationprocess. In embodiments of the invention, the lens and the LED emittersare properly aligned. Further, circuit sheet 130 includes interconnectconductors that are also aligned with emitter substrate sheet 140.

In flexible electronics, electronic circuits can be formed by mountingelectronic devices on flexible plastic substrates, such as polyimide,PEEK or transparent conductive Polyester film. Additionally, flexcircuits can be screen printed silver circuits on polyester. Flexibleelectronic assemblies can often be manufactured using identicalcomponents as those used for rigid printed circuit boards, allowing theboard to conform to a desired shape, or to flex during its use. Asdescribed above, in embodiments of the present invention, the componentsfor multiple LED emitters are formed in sheets of materials. In someembodiments, phosphor sheet 120, circuit sheet 130, and protective sheet150 can be made of flexible and stretchable material, and lens sheet 110and emitter sheet 140 can be rigid with pre-formed notches or cracks.After singulation, the emitters and lenses for individual emitters areheld together by the flexible and stretchable layers as described above.The interconnects in circuit layer 130 can be formed in zig-zag shapesto allow movement of the LED emitters when the substrate is flexed orstretched. Depending on the embodiments, phosphor sheet 120, circuitsheet 130, and protective sheet 150 can be made of flexible,stretchable, or flexible and stretchable materials.

As described above, flexible, stretchable, or flexible and stretchable,sheets of LED emitters can be made using the method and structuresprovided by embodiments of the present invention. Embodiments of thepresent invention can provide one or more of the following benefits overconventional techniques. For example, the methods and structures can beused in mass production of LED emitters, lowering the manufacturingcost. In some embodiments, the singulated emitters can be separated bycutting the remaining sheets. In other embodiments, the flexible,stretchable, or flexible and stretchable sheets of LED emitters can beused in different applications. These applications includes flat panels,wall lighting (e.g., the sheet of LED emitters cab be pasted on targetarea), lighting on a non-flat surface, clothing (signage on jackets orshirts signage for safety, for example). In other embodiments, theemitter sheets also can find applications in traffic control. Forexample, the emitter sheets can be disposed at road side or even as partof the pavement for providing lighting or traffic signs.

In the above description, specific circuits and examples are used toillustrate the embodiments, it is understood that the examples andembodiments described herein are for illustrative purposes only and thatvarious modifications or changes in light thereof will be suggested topersons skilled in the art and are to be included within the spirit andpurview of this invention.

What is claimed is:
 1. A flexible sheet of light-emitting diode (LED)light emitters, comprising: a support substrate including a thermallyconductive material; an LED emitter sheet overlying the supportsubstrate, the LED emitter sheet including a plurality of LED lightemitters; a flexible circuit sheet overlying the LED emitter sheet; aphosphor sheet overlying flexible circuit sheet, the phosphor sheetincluding a wave-length converting material; and a lens sheet overlyingthe phosphor sheet, the lens sheet including a plurality of lenses. 2.The flexible sheet of LED light emitters of claim 1, wherein theflexible sheet of LED emitters is also stretchable.
 3. The flexiblesheet of LED light emitters of claim 1, wherein each of the plurality oflenses in the lens sheet is aligned to a corresponding one of theplurality of LED light emitters.
 4. The flexible sheet of LED lightemitters of claim 1, wherein the lens sheet comprises pre-formed notchesbetween adjacent lenses.
 5. The flexible sheet of LED light emitters ofclaim 1, wherein the LED emitter sheet comprises a ceramic substratewith pre-formed notches between adjacent emitters.
 6. The flexible sheetof LED light emitters of claim 1, wherein the lens sheet comprisesseparate lenses.
 7. The flexible sheet of LED light emitters of claim 1,wherein the LED emitter sheet comprises separate LED emitters.
 8. Theflexible sheet of LED light emitters of claim 1, wherein the pluralityof LED light emitters are inorganic solid-state based LED light sources.9. A flexible sheet of light-emitting diode (LED) light emitters,comprising a stack of sheets including a lens sheet, a phosphor sheet, aflexible circuit sheet, an LED emitter sheet, and a support substratesheet, wherein: the support substrate sheet includes a thermallyconductive material; the LED emitter sheet includes a plurality of LEDlight emitters; the flexible circuit sheet includes conductive wires;the phosphor sheet includes a wave-length converting material; and thelens sheet includes a plurality of lenses.
 10. The flexible sheet of LEDlight emitters of claim 9, wherein each of the plurality of lenses inthe lens sheet is aligned to a corresponding one of the plurality of LEDlight emitters.
 11. The flexible sheet of LED light emitters of claim 9,wherein the lens sheet comprises pre-formed notches between adjacentlenses.
 12. The flexible sheet of LED light emitters of claim 9, whereinthe LED emitter sheet comprises a ceramic substrate sheet withpre-formed notches between adjacent emitters.
 13. The flexible sheet ofLED light emitters of claim 9, wherein the flexible sheet of LED lightemitters is also stretchable.
 14. The flexible sheet of LED lightemitters of claim 9, wherein the flexible circuit sheet is alsostretchable.
 15. The flexible sheet of LED light emitters of claim 14,wherein the flexible circuit sheet comprises conductive wires that arein zig-zag form.
 16. The flexible sheet of LED light emitters of claim9, wherein the plurality of LED light emitters are inorganic solid-statebased LED light sources.
 17. The flexible sheet of LED light emitters ofclaim 9, wherein the flexible circuit sheet is disposed under theplurality of LED light emitters.
 18. The flexible sheet of LED lightemitters of claim 9, wherein the flexible circuit sheet is disposed overthe plurality of LED light emitters.
 19. The flexible sheet of LED lightemitters of claim 9, wherein the flexible circuit sheet is disposedunder the plurality of LED light emitters, and a second flexible circuitsheet is disposed over the plurality of LED light emitters.
 20. Aflexible sheet of light-emitting diode (LED) light emitters, comprisinga stack of sheets including a lens sheet, a phosphor sheet, a flexiblecircuit sheet, and an LED emitter sheet, wherein: the LED emitter sheetincludes a plurality of LED light emitters; the flexible circuit sheetincludes conductive wires; the phosphor sheet includes a wave-lengthconverting material; and the lens sheet includes a plurality of lenses.21. The flexible sheet of LED light emitters of claim 20, furthercomprising a support substrate sheet.
 22. The flexible sheet of LEDlight emitters of claim 21, wherein the support substrate sheetcomprises a thermally conductive material.
 23. The flexible sheet of LEDlight emitters of claim 21, wherein the support substrate sheet isdisposed under the LED emitter sheet.